Hydrorefining of petroleum wax fractions



United States Patent 3,365,385 HYDROREFINING 0F PETROLEUM WAX FRACTIONSNicholas L. Kay and Edward A. Pullen, Fullerton, and Cloyd P. Reeg,Orange, Calif., assignors to Union Oil Company of California, LosAngeles, Calif a corporation of California No Drawing.Continuation-impart of application Ser. No. 131,063, Aug. 11, 1961. Thisapplication Oct. 6, 1964, Ser. No. 401,966

6 Claims. (Cl. 208-27) This application is a continuation-in-part ofapplication Ser. No. 131,063, filed Aug. 11, 1961, now abandoned.

This invention relates to methods for refining crude microwax petrolatumderived as bottoms from the vacuum distillation of full-range petroleumwaxes, and more particularly is concerned with the manufacture ofmicrocrystalline Wax characterized by excellent stability and colorcharacteristics. In broad aspect, the process involves a catalytichydrogenation, or hydrofining technique wherein the process variables,i.e., pressure, temperature, space velocity, etc., are correlated withinspecific ranges in order to effect the desired decolorization withoutappreciable cracking or isomerization. The hydrogenation techniqueinvolves a flooded-bed contacting, such as may be obtained by concurrentupfiow of hydrogen and the liquid wax fraction through the catalyst bed.An important feature of the invention resides in the use of low spacevelocities, i.e., below about 0.4, and preferably below about 0.25. Theuse of low space velocities has been found to be critical to theattaining of a suitably decolorized and stable product under processconditions sufficiently economical for use in connection with theparticular feedstock involved. The flooded-bed contacting feature of theinvention is also correlated with overall economics, as will be moreparticularly pointed out hereinafter.

The feedstocks treated herein are obtained as residue from the vacuumdistillation of the total wax fraction recovered from deasphalted crudeoil residua. The overhead from such distillation constitutes slack wax,from which commercial parafiin Wax is derived. The bottom fraction,referred to herein as petroleum, is ordinarily of a dark brown to blackcolor, and contains from about 20% to 90% microcrystalline wax. It maybe subjected to a deoiling treatment to produce the product commonlyreferred to as microcrystalline wax, or microwax.This microwax hasbecome an important article of commerce, and is used in the manufactureof many products including food containers, wax paper, explosives,matches, etc.

Several methods have previously been suggested for refining anddecolorizing petroleum wax fractions. Perhaps the most widely usedprocess involves contacting such fractions with adsorbent materials suchas alumina, silica gel, clay, activated carbon, or the like. Morerecently, various hydrogenation techniques have been suggested. Whilethe hydrogenation technique is in many respects preferable to theadsorption techniques, its area of usefulness has been fairly limited inthe field of wax refining. In order to obtain acceptable run lengths andcatalyst life, feedstocks have been limited mainly to refined distillateparaifin waxes, or full-range wax fractions which have been subjected toconsiderable pre-refinement, as by deasphalting, de-oiling, etc. Stockssuch as these are relatively light in color, and contain relatively lowconcentrations of catalyst-deactivating compounds such as asphaltenes,condensed-ring aromatic compounds, heavy polyolefins and the like.

In developing the process of this invention, it was recognized at theoutset that the heavier, more highly contaminated and darker coloredresidual petroleum feeddrogenation conditions for effectivedecolorization. The basic problem involved the selection of a propercombinatron of catalyst and hydrogenation conditions, mainly ofpressure, temperature and space velocity, which would give the desireddecolorization without rapid catalyst deactivation and without bringingabout more fundamental changes in hydrocarbon structure, as by cracking,isomerization and the like. Economic considerations were also a primaryfactor.

To understand the economic factors involved in the hydrorefining orrnicrowax fractions, it must be appreciated firstly that these fractionsconstitute a relatively minor volume of total refinery products, andtherefore large and expensive hydrogenation facilities are normally notwarranted. Perhaps the principal factors which contribute to the expenseof hydrogenation facilities center about the use of high pressures,above about 1,000 p.s.i.g.,

. insuring a relatively longer residence time for the liquid.

and the use of very low space velocities which necessitate largereactors and large catalyst volumes per barrel of feed treated. The useof high pressures involves at least two component items of expense,viz., a source of highpressure hydrogen, and the expensive, heavy-walledreactors required. It was hence highly desirable to devise a processwhich could succesfully utilize the low pressure oif-gases fromconventional hydrorefining and/ or reforming units without repressuring,i.e., at pressures below about 900 p.s.i.g.

In conventional hydrorefining operations on naphtha and gas oil feeds,wherein the primary objective is to reduce the sulfur and nitrogencontents, economically attractive space velocities are normally obtainedby operating at relatively high temperatures, e.g., above about 750 F.In the case of petrolatum feeds, however, it has been found thatsatisfactory decolorization at pressures below about 900 p.s.i.g. is notnormally obtainable at temperatures above about 750 P. But, operating atlower temperatures leads to the economically undesirable alternatives ofusing high pressures, or very low space velocities. The presentinvention is based upon our discovery that the microwax petrolatum feedsmay be satisfactorily decolorized at temperatures of 600 to 750 F., andat pressures below about 900 p.s.i.g., if the space velocity ismaintained at between about 0.05 and 0.4, and if the residence time ofthe liquid phase is maximized by using the flooded-bed contactingtechnique. Without the floodedbed technique, even lower space velocitieswould be required, necessitating the use of prohibitively large reactorsand catalyst volumes. Thus, by utilizing either concurrent upflow offeedstock and hydrogen, or countercurrent downflow of feed with upfiowof hydrogen, a liquid level can be maintained in the catalyst bed,thereby phase than would prevail at the same space velocity in aconventional downfiow reactor. The effectiveness of increased residencetime came as somewhat of a surprise. since residence time per se isnormally a relatively insignificant factor in heterogeneous catalysis,total throughput rate, or liquid hourly space velocity, being theprincipal significant variable.

From the above, it will be apparent that the principal objective of thisinvention is to provide an economically attractive hydrofining treatmentfor residual microwax feedstocks, utilizing relatively low temperaturesand pressures. A more specific objective is to minimize the economicallyundesirable effects of operating at extremely low space velocities. Theoverall objective is to provide a low temperature, low pressurehydrofining operation for decolorizing residual microwax feeds,utilizing a minstocks to be treated would require relatively severehyimum catalyst volume and reactor space. A further objective is toprovide methods for decolorizing microwax feeds while maintainingsatisfactory catalyst activity for at least about 10 days betweenregenerations without re- 3 sorting to expensive preliminary refiningas, e.g., by deasphaltlng. Other objectives will be apparent from themore detailed description which follows.

The following flow diagram illustrates the derivation of the petrolatumfeedstocks treated herein:

CRUDE OIL RESIDUUM I Duo-Sol-Extraction Aron-.atie aspbaltic extraatWaxy paratllnic Raillnate Petrolatum Bottoms In Step I, Duo-Solextraction is performed by countercurrent extraction with propane and aphenolic solvent such as cresylic acids. Dewaxing Step II is aconventional propane dewaxing wherein the propane raffinate from Step Ii chilled with concurrent evaporation of propane to precipitate thetotal wax component. Vacuum distillation Step III is carried out atreduced pressures of, e.g., 2-50 mm. of mercury, and at pot temperaturesin the range of about 550-720 F. During this distillation, low-meltingparaffin waxes boiling below about 600 F. (2 mm.) are taken overhead.The residual microwax petrolatum boils above about 500 F. at 2 mm., anddue to the substantially complete removal of paraffin wax, and also tothermal degradation occurring at the maximum temperatures reached in thereboiler, is very dark in color and rich in condensed polycyclics.

For purposes of this invention, the critical characterizations of thepetrolatum feedstocks relate to color, boiling range and polyaromaticcontent. Quantitative color determinations are rendered somewhatdiflicult because these feedstocks are so dark in color that they areoff the conventional color scales. Under these circumstances, colordeterminations can be made only by diluting the sample with awater-white diluent such as kerosene. Two well known color scales in thedark range are the Tag- Robinson scale and the ASTM D-l500 scale, whichcorrelate as follows:

Tag-Robinson: ASTM D-l 500 21 1 0.5

1 Pale yellow.

2 Dark brown.

The petrolatum feeds of this invention are characterized as being darkerthan 1.0 on the Tag-Robinson scale and darker than 8 on the ASTM scale,even when diluted to form a 25 vol. percent solution in kerosene. Inmost cases, even a solution in kerosene is off both color scales. Theprincipal objective of the hydrofining treatment is to reduce the colorto a maximum of 3.0 on the ASTM scale in order to meet requirements setby the Food and Drug Administration for waxes to be used in foodpackaging containers. The hydrofining process described herein is foundto achieve this objective without resort to expensive preliminaryrefining measures such as deasphalting, which have been consideredessential in the past when dealing with refractory feeds of this nature.

Polyaromatic content (or carbonizable matter content) of the petrolatumfeeds is directly reflected by the absorption coefficient for ultraviolet radiation in the 290330 millimicron wave length band. Theabsorption coefiicient of the feeds treated herein ranges between about1.0 and 3.5 liters/gm. cm. at wave lengths in the 290330 millimicronrange.

In other respects, the petrolatum feeds may be characterized as boilingbetween about 500 and 700 F. at 2 mm. of mercury and as having aspecific gravity between about 0.81 and 0.85, an ASTM D938 congealingpoint between about and F., a refractive index (at 100 C.) between about1.45 and 1.46, and an oil content of about 550% by weight. It ispreferred to subject the petrolatum directly to hydrofining, becauseduring hydrofining a small amount of oil is usually formed, requiring asubsequent deoiling step. It is therefore preferable to postpone thefinal deoiling until after the hydrofining treatment.

The hydrofining operation is carried out in a conventional reactorcontaining a fixed bed of granular catalyst. Preferably, the catalyst isin a somewhat more finely subdivided state than is normal, as forexample ,-inch pellets, or 8 to 20 mesh granules. The feedstock ispreheated to the desired hydrofining temperature, and pumped through thereactor, either upfiow or downflow. If the upfiow procedure is employed,the hydrogen is pumped concurrently upwardly along with the feed, andthis inherently will maintain the catalyst bed submerged in liquid feed,i.e., the feed will form a substantially continuous phase, filling theinterstices between the catalyst granules. If the feed is passeddownwardly through the catalyst bed, the hydrogen is then pumpedupwardly countercurrently. The desired liquid level (preferablysubmerging the entire bed) is maintained by means of aliquid-level-controlled outlet valve at the bottom of the reactor.Hydrogen gas is pumped in near the bottom of the reactor and bubblesupwardly therethrough, and is removed from the top of the reactor. Ineither type of operation, it is found that suitable process conditionsfall within the following ranges:

It will be understood that these conditions should be properlycorrelated. For optimum results, temperatures above 700 F. will normallybe used only at higher pressures, i.e., above about 700 p.s.i.g., andtemperatures below about 650 F. would be used in conjunction with spacevelocities below about 0.25 and pressures between about 300-600 p.s.i.g.

Suitable hydrofining catalysts for use herein include in general any ofthe Group V-IB and/or Group VIII metals, their oxides and sulfides,either as such, or preferably supported upon an adsorbent oxide carriersuch as alumina, titania, zirconia, silica gel, activated clays and thelike. Particularly suitable catalysts comprise a combination of aniron-group metal oxide or sulfide (preferably an oxide or sulfide ofcobalt or nickel) with a Group VIB metal oxide or sulfide (preferably anoxide or sulfide of molybdenum or tungsten). Preferred supports areactivated alumina, or activated alumina stabilized by the addition of asmall proportion (3%-15%) of silica gel. The total hydrogenatingcomponents may comprise between about 4% and 25% by weight of thefinished catalyst. Preferred catalysts are the cobalt molybdate type,which contain between about 1% and 5% cobalt oxide or sulfide, andbetween about 5% and 20% (by weight) molybdenum oxide or sulfide.Preferably the catalyst is subjected to a presulfiding technique inorder to convert the active hydrogenating components substantiallycompletely to sulfide forms.

According to one modification to the process, a substantially inertdiluent oil may be added to the petrolatum feed. Suitable diluent oilsinclude for example light mineral oil frac tions, kerosene, jet fuelfractions and the like. The principal function of the diluent is tolower the viscosity of the feed, thereby improving diffusion rates. Itmay also increase the solubility of hydrogen in the liquid feed.Moreover, vaporization of the diluent in the reactor may assist inproviding additional agitation with resultant improved contactingefiiciency. Particularly preferred diluents are those boiling in thekerosene range. Suitable proportions of diluent may range between about10% and 80% by volume of the final mixture. i i

In order to obtain run lengths greater than about 30 days betweencatalyst regenerations, another technique has been found to be useful,namely, a periodic flushing of the catalyst with hydrogen. This ispreferably achieved by simply interrupting the flow of feedstock every7-10 days, while all-owing hydrogen to continue flowing through thecatalyst bed under process conditions for about 4-12 hours.

The following examples are cited to illustrate the critical effects ofthe process variables prescribed herein, and suitable operatingprocedures, but are not to be construed as limiting in scope:

EXAMPLE I This example demonstrates the efiicacy of upfiow vs. downflowin wax hydrofining. The feed was a partially refined paraffin wax havinga melting point of 158 F. and an ASTM D15*00 color of 4.0. In all runs,the catalyst was a presulfided composite of 3% C and 15% M00 impregnatedupon a pelleted SiO 95% Al 0 carrier. All runs were carried out at 550F. and 0.5 space velocity, using 1,000 s.c.f. of hydrogen per barrel offeed. In one series of runs (Series A) the preheated mixture of feed andhydrogen was passed downwardly through the catalyst bed, while inanother series (Series B), the preheated mixture was passed upwardly soas to maintain the entire catalyst bed submerged in liquid feed, withhydrogen bubbling upwardly therethrough. The results were as follows:

TABLE 2 Color of Product, ASTM D-1500 Pressure, p.s.i.g.

Run Series A, Run Series B,

Downflow Upfiow 1 L 0. 5 2. 5 L 0. 5 2. 5 L 0. 5 2. 5 L 0. 5

l Prefix L means lighter than the designated number, but darker than thenext lower point on the scale.

EXAMPLE II This example demonstrates the critical effects of spacevelocity in treating an undistilled microwax. The feed was amicrocrystalline wax (1.2% oil) having an ASTM D-938 melting point ofabout F. and an ASTM Dl500 color darker than 8.0 even when diluted with3 volumes of kerosene. The entire run was carried out at 675 F., and 450p.s.i.g., using 1,000 s.c. f. of hydrogen per barrel of feed, but theliquid hourly space velocity was varied at several intervals. The flowof feed and hydrogen was upward, and the catalyst was the same as inExample I, except that it was ground to 8-12 mesh particle size. Productsamples were collected at l-hour intervals. The results were as follows:

TABLE 3 Catalyst Age, LHSV Color, ASTM Oil content, wt.

Hours D-1500 percent, D721 1. 0 L 1. 5 1. 0 2.0 1. 0 2. 5 1.0 3.0 1. 03. 5 O. 5 4. 0 0. 5 3. 0 0. 5 3.0 0. 5 L 3. 0 0. 5 L 3.0 0. 5 L 3.0 0.25 2. 5 0.25 L 2. 0 0.25 L 2.0 0.25 L 2.0 1. 0 3. 0 1.0 4. 5 1. 0 4.5 1. 0 L 5.0

From the foregoing data, it will be apparent that sustained and adequatedecolorization was not obtainable except at space velocities below about0.5. The initial high activity of the fresh catalyst at 1.0 spacevelocity soon declined, and on returning to the 1.0 space velocity after24 hours on stream, the marked difference between operating at 0.25 and1.0 space velocity is more readily apparent, the catalyst then havingreached its equilibrium activity. a

This example also demonstrates, in view of the significant though notexcessive oil-synthesis, that deoilin-g should preferably be postponeduntil after the hydrotfining operation.

EXAMPLE III Another run was carried out which demonstrates thatdeclining catalyst activity cannot be compensated for by raising thetemperature above the optimum limits at the particular pressure used.The feed was a 50/50 mixture of a light mineral oil diluent and a crudepetrolatum (17% oil) having an ASTM D938 melting point of 158 F., acolor darker than 8.0 on the ASTM D-1500 color scale when diluted to 15%concentration in kerosene, and an absorption coefficient of 1.88 at the290 millimicron wave length. The catalyst was the same as that employedin Example I, except that it was ground to 10-20 mesh particle size.After 50 hours on stream, (concurrent upfiow) and at 450 p.s.i.g., 0.2LHSV, 675 F., and 1,000 s.c.f. of hydrogen per barrel of feed, the colorof the undiluted petrolatum product was 3.5 on the ASTM D-1500 colorscale. An attempt was made to improve the color by raising thetemperature to 700 F., but

at this low pressure, the color did not improve, but instead declined to4.0 at the 58th hour on stream.

EXAMPLE IV This example illustrates suitable operating conditions forextended run lengths of up to about 30-40 days. The catalyst was thesame as in Example III, and the same petrolatum feed was used, but wasdiluted with 50 kerosene. The kerosene diluent is believed to beadvantageous in providing increased hydrogen solubility in the feed,

decreased viscosity and increased agitation, as previously noted. Runconditions were as follows:

Contacting technique.Cncurrcnt upflow H /oil ratio, s.c.f./bbl. 1,000

The color of the undiluted product at the 18th hour of operation was0.5, and at the end of 200 hours, about 2.5. During the run, it wasfound that the catalyst activity could be partially revived byperiodically flushing with hydrogen, and/or by gradually lowering thespace velocity, satisfactory decolorization can be maintained for runlengths of 30-40 days, after which the catalyst can be regenerated byconventional oxidation techniques.

The foregoing description of specific methods, catalysts and feeds isnot intended to be limiting except where indicated. Many variations willoccur to those skilled in the art, and all such variations which yieldessentially the same result are intended to be included. The true scopeof the invention is intended to be embraced within the following claims.

We claim:

1. A method for decolorizing a microwax petrolatum feedstock to a valuebelow about 3.0 on the ASTM D- 1500 color scale, said feedstockconsisting essentially of undistilled bottoms from the vacuumdistillation of a full-range petroleum wax fraction, and beingcharacterized by: (1) a boiling range above about 500 F. at 2 mm., (2)an ASTM D-1500 color darker than 8 when diluted with three volumes ofkerosene, and (3) an ultra violet absorption coefiicient between about1.0 and 3.5 at 290 millimicrons, which comprises continuously passingsaid feedstock in liquid-phase through a catalytic hydrofining zone withadded hydrogen in contact with a fixed bed of granular hydrofiningcatalyst at a temperature between about 600 and 750 F., a pressurebetween about 300 and 900 p.s.i.g. and a liquid hourly space velocitybetween about 0.05 and 0.4, while maintaining said bed of catalystsubmerged in a substantially continuous phase of liquid feed withhydrogen passing upwardly therethrough, continuing said contacting for aperiod of at least about 10 days without regenerating said catalystwhile correlating said hydrofining conditions to produce continuously amicrowax product having an ASTM D1500 color lgihter than about 3.0, saidhydrofining catalyst being in the form of granules of size between aboutinch and 8 mesh and comprising a granular carrier consisting essentiallyof alumina upon which is deposited minor proportions of a Group VIBmetal and an iron-group metal in the form of sulfides and/or oxides.

2. A process as defined in claim 1 wherein said catalyst bed ismaintained substantially submerged in feed by flowing both feed andhydrogen concurrently upwardly therethrough.

3. A process as defined in claim 1 wherein said catalyst bed ismaintained substantially submerged in feed by flowing said feeddownwardly, and said hydrogen countercurrently upwardly therethrough,and controlling the rate of withdrawal of liquid product so as tomaintain a liquid level in the contacting zone.

4. A process as defined in claim 1 wherein said hydrofining catalyst isa sulfided composite of cobalt and molybdenum oxide supported on acarrier which is essentially activated alumina.

5. A process as defined in claim 1 wherein said hydrofining is carriedout in the presence of a light petroleum distillate diluent for saidfeedstock.

6. A process as defined in claim 1 wherein said hydrofining is carriedout at a temperature between about 625 and 700 F., a pressure betweenabout 400 and 750 p.s.i.g. and a liquid hourly space velocity betweenabout 0.1 and 0.25.

References Cited UNITED STATES PATENTS 2,773,110 12/1956 Luben 208272,846,356 8/1958 Mills et al. 20827 2,956,001 10/1960 Spars et al. 208272,998,377 8/1961 Beuther et al. 20827 3,089,841 5/1963 Berkowitz 208273,119,762 1/1964 Siegmund 208-27 PATRICK P. GARVIN, Primary Examiner.

DANIEL E. WYMAN, Examiner.

P. E. KONOPKA, Assistant Examiner.

1. A METHOD FOR DECOLORIZING A MICROWAX PETROLATUM FEEDSTOCK TO A VALUEBELOW ABOUT 3.0 ON THE ASTM D1500 COLOR SCALE, SAID FEEDSTOCK CONSISTINGESSENTIALLY OF UNDISTILLED BOTTOMS FROM THE VACUUM DISTILLATION OF AFULL-RANGE PETROLEUM WAX FRACTION, AND BEING CHARACTERIZED BY: (1) ABOILING RANGE ABOVE ABOUT 500*F. AT 2 MM., (2) AN ASTM-D-1500 COLORDARKER THAN 8 WHEN DILUTED WITH THREE VOLUMES OF KEROSENE, AND (3) ANULTRA VIOLET ABSORPTION COEFFICIENT BETWEEN ABOUT 1.0 AND 3.5 AT 290MILIMICRONS, WHICH COMPRISES CONTINUOUSLY PASSING SAID FEEDSTOCK ISLIQUID-PHASE THROUGH A CATALYTIC FIXED BED OF GRANULAR HYDROFININGCATALYST AT A TEMPERATURE BETWEEN ABOUT 600*F AND 750*F., A PRESSUREBETWEEN ABOUT 300 AND 900 P.S.I.G. AND A LIQUID HOURLY SPACE VELOCITYBETWEEN ABOUT 0.05 AND 0.4, WHILE MAINTAINING SAID BED OF CATALYSTSUBMERGED IN A SUBSTANTIALLY CONTINUOUS PHASE OF LIQUID FEED WITHHYDROGEN PASSING UPWARDLY THERETHROUGH, CONTINUING SAID CONTACTING FOR APERIOD OF AT LEAST ABOUT 10 DAYS WITHOUT REGENERATING SAID CATALYSTWHILE CORRELATING SAID HYDROFINING CONDITIONS TO PRODUCE CONTINUOUSLY AMICROWAX PRODUCT HAVING AN ASTM D-1500 COLOR LIGHTER THAN ABOUT 3.0,SAID HYDROFINING CATALYST BEING IN THE FORM OF GRANULES OF SIZE BETWEENABOUT 1/16 INCH AND 8 MESH AND COMPRISING A GRANULAR CARRIER CONSISTINGESSENTIALLY OF ALUMINA UPON WHICH IS DEPOSITED MINOR PROPORTIONS OF AGROUP VIB METAL AND AN IRON-GROUP METAL IN THE FORM OF SULFIDES AND/OROXIDES.